The present invention relates generally to improved methods for taking impressions of the feet and then forming custom-made shoe inserts in conformance with those foot impressions, and more particularly, to forming full-length impressions of the feet that are useful in the process of forming shoe inserts suitable for providing accurate full foot length support for a consumer's feet when inserted into that consumer's shoes in order to produce semi-custom footwear solely intended for him or her.
One known method of taking foot impressions wherein a person steps onto a foot impression unit comprising a bed of pneumatically supported pins is disclosed in U.S. Pat. No. 4,876,758 dated Oct. 31, 1989 and entitled “System and Method for Forming Custom-Made Shoe Inserts” by Paul D. Rolloff et al, and assigned to Amfit Inc. then located in Sunnyvale, Calif. and now located in Santa Clara, Calif. In detail, this method of taking foot impressions comprises the steps of: applying pneumatic support to the bed of pins; stepping onto the bed of pins; locking the pins in place; digitally recording and storing positions of the pins thereby generating a digitally recorded negative model of the person's foot contour as impressed in the pins; and then forming shoe inserts in a “shaping unit” in nominal conformance with the digitally recorded negative model of the person's foot contour as impressed in the pins. Another method of making foot impressions wherein a person steps into crushable foam media contained within a simple rectangular box is also known.
Unfortunately, neither of these methods is very accurate. This is primarily because in either case all portions of the feet are subjected to essentially the same supporting pressure with the result that foot displacement is limited only by the heel and other bony weight bearing structure physically coming in contact with a rigid supporting structure. This results in macro foot impression errors wherein the bony weight bearing structure is substantially coplanar while soft tissue portions of the feet are positioned in an indeterminate manner. However, because of further reference made below to the '758 patent, it is expressly incorporated herein by reference.
In a totally different vein, most podiatrists insist that the only proper way to take an accurate foot impression is to “lock” the metatarsus of a foot in position and then form a negative casting of trailing portions of the foot while it is in that locked position. Typically, the metatarsus is so locked by forcibly elevating the lessor toes while the casting process is ongoing. Then a positive casting is made from the negative casting. Next a rigid or semi-rigid insert conforming to trailing foot portions of the positive casting is made. Generally, rigid or semi-rigid inserts are formed of a thermoplastic material wherein sheets of the thermoplastic material are draped over such positive castings in an oven and allowed to conform to the positive castings of their own weight and thus generate trailing portion semi-finished rigid or semi-rigid inserts. After the semi-finished rigid or semi-rigid inserts are removed from the oven and cut to size, they are usually combined with full foot length layers of compliant material and hand formed into a pair of shoe inserts the podiatrists refer to as “orthotics”.
There are two serious problems with the above-described procedure utilized by the podiatrists. Most obviously, the process doesn't include any modeling the forefoot portions of the feet at all. As a result, no corrective provision can be made for relatively common maladies such as pronation wherein the great toe metatarsal head should be elevated, or Morton's toe wherein at least the second metatarsal head is more forwardly positioned and usually depressed relative to the first metatarsal head.
Even more seriously however, the podiatrist is actually distorting the foot as he or she forcibly elevates the lessor toes. The metatarsus is locked in a position wherein the fifth and perhaps even the fourth metatarsals are elevated and the first is severely depressed. This results in the first or great metatarsal head being significantly depressed which in turn results in an exaggerated arch. It also results in excessive relative roll axis distortion in the placement of the heel with reference to the metatarsal heads where an axis through the metatarsal heads falls inward even as the heel rolls outward. This can lead to all sorts of leg, hip and back problems. In fact, the above described process is flawed to such a degree that it is common for podiatrists to purposely introduce impression errors such as by adding additional metatarsal support in an effort to overcome anticipated complaints by their patients. It is even common to encounter podiatrists adding wads of adhesive backed cotton to metatarsal areas of seriously flawed shoe inserts.
A far more accurate hand method of taking a person's full-length foot impressions was disclosed in U.S. Pat. No. 4,155,180 dated May 22, 1979 and entitled “Footwear for More Efficient Running”. In detail, the hand method of taking full-length foot impressions described in the '180 patent comprised the steps of: stacking two pieces of elastomeric polyurethane foam media having a density of about 5 lbs./cu.ft. with the upper piece being about 1 inch thick and the lower piece being about 3 inches thick; stretching a first sheet of flexible plastic film material of about 0.001 inch thickness over the top piece of elastomeric polyurethane foam media; pouring a pool of plaster of Paris casting material in the center portion of the flexible plastic film material; stretching a second sheet of the plastic film material over the plaster of Paris; the person stepping into the second sheet of plastic film material covering the plaster of Paris; the person holding this position until the plaster of Paris solidifies thus forming a negative casting of his or her feet; the person carefully removing his or her weight and feet from the platform; and utilizing the negative casting as a mold for forming a positive casting of his or her feet. The positive casting was then utilized in a hand process of making a pair of shoe inserts therefrom as further described in the '180 patent.
However, in actual practice it was very difficult to form the negative casting without cracking it. Furthermore, even though the elastomeric polyurethane foam media supported the feet in a substantially linear manner as specifically opposed to the non-linear support provided by either of the foot impression unit of the '758 patent or the crushable foam media, the relatively large thickness of the two superimposed pieces thereof in combination with inadequate load bearing capability of the toes still resulted in outer forefoot portions of the feet being displaced upward from their preferred positions. As a consequence of such foot impression flaws, forming shoe inserts by this process entailed considerable handwork and was thus problematic. As a result of these practical problems, the procedure disclosed in the '180 patent was never reduced to practice commercially.
As a result of the various flaws inherent in all of the other above described procedures and similar flaws involved in other known procedures not specifically mentioned hereinabove, many individuals have found it necessary to modify their shoe inserts in order to get successful results. In particular, this includes runners who must selectively build up or relieve various portions of their shoe inserts in order to avoid foot, knee, leg, hip and/or lower back pain when running. Depending upon which type of shoe insert the individual has, such modifications can include mid-foot and/or arch areas, and/or areas just forward of the metatarsal heads and under the toes. Such modifications are of course most undesirable because of the obvious inaccuracies involved.
It is in fact believed herein that it is simply not possible to obtain really acceptable shoe inserts from any source at this time. For instance, the present inventor has in his possession commercially and professionally obtained shoe inserts such as those mentioned above, as well as positive castings from which his “orthotics” were made and positive castings made from his foot impressions formed in crushable foam media. None of these shoe inserts or positive castings remotely conform to one another and all are in equally gross non-conformance with various foot inserts made for a range of activities according to the teachings presented hereinbelow and believed herein to support the present inventor's feet in as anatomically correct a manner as is possible for the respective activities.
It has been found that no one set of shoe inserts is optimum for use in all shoes or for all activities. Firstly, various brands and types of shoes are made on different lasts, and their resulting different internal shapes deleteriously modify foot support derived from any presently known type of shoe insert. Secondly, feet dynamically change shape depending upon their instant disposition. Thus, shoe insert contours optimally formed for relatively sedentary activities such as walking are totally unsuited for more dynamic activities such as running.
The object of the present invention then, is to provide apparatus and methods for implementing more accurate and reproducible foot impressions and for forming shoe inserts of generally improved composite contours having specific application targeted geometries that are practical for manufacture and thus suitable for sale and distribution to consumers.